Lutz Creek watershed,Barro Colorado Island,Republic of Panama     

Matthew C. Larsen PhD  Robert F. Stallard PhD  Steven Paton MS 《水文研究》2021,35(4):e14157

Lutz creek is a small (9.69 ha) catchment located on Barro Colorado Island (BCI), a 1500-ha island in Lake Gatún, the principal freshwater reservoir (425 ha, 26 m above sea level) of the Panama Canal watershed in central Panama. In 1972, a concrete V-notch weir was installed on the creek, located at 9°09′42.8358″N, 79°50′15.6699″W, and hydrological record keeping began. The island was first established as a research station in 1923 and precipitation data collection was initiated in 1925. A meteorological tower, installed in 1972 and located a few meters from the weir, is currently instrumented to collect air temperature, relative humidity, wind speed and direction, evapotranspiration and solar radiation. In addition, since 1972, gravimetric soil moisture has been measured at least biweekly at 10 sites located throughout the Lutz Catchment above the location of the weir. Data collection and the administration of BCI are the responsibility of the Smithsonian Tropical Research Institute (STRI; https://stri.si.edu ) which funds the data collection and storage. Data are in the public domain, entitled ‘Lutz Watershed And Meteorological Tower’ and are available at the STRI Physical monitoring website https://biogeodb.stri.si.edu/physical_monitoring/ .  相似文献   

天然实验流域降雨径流现象发生的悖论          下载免费PDF全文

顾慰祖  尚熳廷  翟劭燚  陆家驹  Frentress Jason  Carol Kendall 《水科学进展》2010,21(4):471-478

作为滁州水文实验系统一部分的1号天然实验流域,面积7897m2,以安山岩为基底,上覆平均厚度2.46m的第四系沉积物。实测了包括地面径流和地面下径流的各种降雨径流响应,后者包括来自非饱和带的壤中流和饱和带的地下水径流。表明这些径流成分有着复杂的组合类型,主要是以地面径流为主的SR型和以地面下径流为主的SSR型,以及中间的和演化的类型。SR型实例中的地面径流量可占总径流的65%,而SSR实例中的地面下径流量可有90%。主要降水的7月,地面下贡献占54.5%,其中地下水径流即占33%。大部分地面径流与降水的18O组成有不小的差异,比较了同时进行测验的3个实验流域,在1400min的降水径流过程中,降水的平均δ18O为-1.210%,而同期地面径流的平均δ18O,2号水文山流域(512m2)为-1.132%,1号南大洼天然流域为-1.065%,3号只有薄层风化碎屑的牵牛花流域(4573m2)为-0.801%。这质疑了现行同位素流量过程线划分方法8个假定中的两个:地面径流的同位素组成不同于降水,天然流域尤其如此;各种水源在汇集过程中的同位素分馏影响并非都可忽略不计。实验流域因降水而产生径流,但所产生的径流却有着非本次降水的组分,这一降水径流悖论发生于各个实验流域。SR型和SSR型总的非本次降水组分分别达16%和64%。  相似文献   

Molybdenum isotope evidence for mild environmental oxygenation before the Great Oxidation Event   总被引：1，自引：0，他引：1  

Yun Duan  Ariel D. Anbar  Timothy W. Lyons  Brian Kendall 《Geochimica et cosmochimica acta》2010,74(23):6655-6668

We use the molybdenum isotope paleoredox proxy to look for evidence of small amounts of O₂ in the environment ∼50 Ma before the Great Oxidation Event (GOE) in a high resolution profile from the ∼2.5 Ga Mt. McRae Shale. The molybdenum isotope compositions (δ^98/95Mo) from samples throughout the sequence span a range from 0.99‰ to 1.86‰. All samples have heavier δ^98/95Mo compared to average upper continental crust. In addition, the upper (S1) and lower (S2) black shale units within the Mt. McRae Shale exhibit systematic differences in average isotopic compositions and distinct patterns of δ^98/95Mo variation. Heavier δ^98/95Mo values occur in the S1 unit, where δ^98/95Mo correlates with Mo enrichments. In the S2 unit, δ^98/95Mo is not as heavy and is relatively invariant.Based on sedimentary Fe proxies we infer that S1 sediments were deposited under euxinic conditions, so that Mo removal from bottom waters was likely quantitative. Thus, δ^98/95Mo in this interval likely records coeval seawater. The lighter δ^98/95Mo values in the S2 unit may indicate a less fractionated ocean Mo inventory relative to the S1 unit. However, sedimentary Fe proxies suggest that S2 sediments accumulated under a water column that was ferruginous rather than euxinic, raising the possibility of non-quantitative Mo scavenging and hence an expressed δ^98/95Mo fractionation relative to coeval seawater. Because any associated fractionations during this process would have favored the light isotope in sediments, the lighter δ^98/95Mo values in the S2 unit represent a lower limit on the value in contemporaneous seawater.After evaluating a range of hypotheses, we conclude that the isotopically heavy δ^98/95Mo values seen throughout the Mt. McRae Shale likely reflect the effects of oxidative weathering and adsorption of Mo to oxide mineral surfaces on land or in surface oceans. The extent of environmental oxygenation in either unit is difficult to assess due to uncertainties in the global Mo isotope budget. Because of the small ocean Mo inventory in the Late Archean, documented by low concentrations of Mo and low Mo/TOC, the extent of oxygenation required to account for the observed fractionations is much smaller than in modern oceans. However, when juxtaposed against the record of δ^98/95Mo through time, our findings provide further evidence of the onset of environmental oxygenation before the GOE.  相似文献   

Characterization of surface and ground water δ18O seasonal variation and its use for estimating groundwater residence times     

Michael M. Reddy  Paul Schuster  Carol Kendall  Micaela B. Reddy 《水文研究》2006,20(8):1753-1772

¹⁸O is an ideal tracer for characterizing hydrological processes because it can be reliably measured in several watershed hydrological compartments. Here, we present multiyear isotopic data, i.e. ¹⁸O variations (δ¹⁸O), for precipitation inputs, surface water and groundwater in the Shingobee River Headwaters Area (SRHA), a well‐instrumented research catchment in north‐central Minnesota. SRHA surface waters exhibit δ¹⁸O seasonal variations similar to those of groundwaters, and seasonal δ¹⁸O variations plotted versus time fit seasonal sine functions. These seasonal δ¹⁸O variations were interpreted to estimate surface water and groundwater mean residence times (MRTs) at sampling locations near topographically closed‐basin lakes. MRT variations of about 1 to 16 years have been estimated over an area covering about 9 km² from the basin boundary to the most downgradient well. Estimated MRT error (±0·3 to ±0·7 years) is small for short MRTs and is much larger (±10 years) for a well with an MRT (16 years) near the limit of the method. Groundwater transit time estimates based on Darcy's law, tritium content, and the seasonal δ¹⁸O amplitude approach appear to be consistent within the limits of each method. The results from this study suggest that use of the δ¹⁸O seasonal variation method to determine MRTs can help assess groundwater recharge areas in small headwaters catchments. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

A Hybrid Statistical-Dynamical Downscaling of Air Temperature over Scandinavia Using the WRF Model     

Jianfeng WANG  Ricardo M. FONSECA  Kendall RUTLEDGE  Javier MARTíN-TORRES  Jun YU 《大气科学进展》2020,37(1):57-74

An accurate simulation of air temperature at local scales is crucial for the vast majority of weather and climate applications.In this work,a hybrid statistical–dynamical downscaling method and a high-resolution dynamical-only downscaling method are applied to daily mean,minimum and maximum air temperatures to investigate the quality of localscale estimates produced by downscaling.These two downscaling approaches are evaluated using station observation data obtained from the Finnish Meteorological Institute over a near-coastal region of western Finland.The dynamical downscaling is performed with the Weather Research and Forecasting(WRF)model,and the statistical downscaling method implemented is the Cumulative Distribution Function-transform(CDF-t).The CDF-t is trained using 20 years of WRF-downscaled Climate Forecast System Reanalysis data over the region at a 3-km spatial resolution for the central month of each season.The performance of the two methods is assessed qualitatively,by inspection of quantile-quantile plots,and quantitatively,through the Cramer-von Mises,mean absolute error,and root-mean-square error diagnostics.The hybrid approach is found to provide significantly more skillful forecasts of the observed daily mean and maximum air temperatures than those of the dynamical-only downscaling(for all seasons).The hybrid method proves to be less computationally expensive,and also to give more skillful temperature forecasts(at least for the Finnish near-coastal region).  相似文献   

Carbon isotope fractionation of dissolved inorganic carbon (DIC) due to outgassing of carbon dioxide from a headwater stream     

Daniel H. Doctor  Carol Kendall  Stephen D. Sebestyen  James B. Shanley  Nobuhito Ohte  Elizabeth W. Boyer 《水文研究》2008,22(14):2410-2423

The stable isotopic composition of dissolved inorganic carbon (δ¹³C‐DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed δ¹³C‐DIC increased between 3–5‰ from the stream source to the outlet weir approximately 0·5 km downstream, concomitant with increasing pH and decreasing PCO₂. An increase in δ¹³C‐DIC of 2·4 ± 0·1‰ per log unit decrease of excess PCO₂ (stream PCO₂ normalized to atmospheric PCO₂) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO₂ outgassing rather than exchange with atmospheric CO₂ may be the primary cause of increased δ¹³C‐DIC values downstream when PCO₂ of surface freshwater exceeds twice the atmospheric CO₂ concentration. Although CO₂ outgassing caused a general increase in stream δ¹³C‐DIC values, points of localized groundwater seepage into the stream were identified by decreases in δ¹³C‐DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO₂ during the early spring growing season. Thus, in spite of effects from CO₂ outgassing, δ¹³C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Brackish marshes erode twice as fast as saline marshes in the Mississippi Delta region     

Kendall Valentine  Grayton Bruno  Tracy Elsey-Quirk  Giulio Mariotti 《地球表面变化过程与地形》2021,46(9):1739-1749

Marsh soil properties vary drastically across estuarine salinity gradients, which can affect soil strength and, consequently, marsh edge erodibility. Here, we quantify how marsh erosion differs between saline and brackish marshes of the Mississippi Delta. We analyzed long-term (1932–2015) maps of marsh loss and developed an algorithm to distinguish edge erosion from interior loss. We found that the edge erosion rate remains nearly constant at decadal timescales, whereas interior loss varies by more than 100%. On average, roughly half of marsh loss can be attributed to edge erosion, the other half to interior loss. Based on data from 42 cores, brackish marsh soils had a lower bulk density (0.17 vs. 0.27 g/cm³), a higher organic content (43% vs. 26%), a lower shear strength (2.0 vs. 2.5 kPa), and a lower shear strength in the root layer (13.8 vs. 20.7 kPa) than saline marsh soils. We then modified an existing marsh edge erosion model by including a salinity-dependent erodibility. By calibrating the erodibility with the observed retreat rates, we found that the brackish marsh is two to three times more erodible than the saline marshes. Overall, this model advances the ability to simulate estuarine systems as a whole, thus transcending the salinity boundaries often used in compartmentalized marsh models.  相似文献   

Detection of multiple fracture sets using observations of shear‐wave splitting in microseismic data     

James P. Verdon  J.‐Michael Kendall 《Geophysical Prospecting》2011,59(4):593-608

The hydrocarbon industry is moving increasingly towards tight sandstone and shale gas resources – reservoirs that require fractures to be produced economically. Therefore, techniques that can identify sets of aligned fractures are becoming more important. Fracture identification is also important in the areas of coal bed methane production, carbon capture and storage (CCS), geothermal energy, nuclear waste storage and mining. In all these settings, stress and pore pressure changes induced by engineering activity can generate or reactivate faults and fractures. P‐ and S‐waves are emitted by such microseismic events, which can be recorded on downhole geophones. The presence of aligned fracture sets generates seismic anisotropy, which can be identified by measuring the splitting of the S‐waves emitted by microseismic events. The raypaths of the S‐waves will have an arbitrary orientation, controlled by the event and geophone locations, meaning that the anisotropy system may only be partly illuminated by the available arrivals. Therefore to reliably interpret such splitting measurements it is necessary to construct models that compare splitting observations with modelled values, allowing the best fitting rock physics parameters to be determined. Commonly, splitting measurements are inverted for one fracture set and rock fabrics with a vertical axis of symmetry. In this paper we address the challenge of identifying multiple aligned fracture sets using splitting measured on microseismic events. We analyse data from the Weyburn CCS‐EOR reservoir, which is known to have multiple fracture sets, and from a hydraulic fracture stimulation, where it is believed that only one set is present. We make splitting measurements on microseismic data recorded on downhole geophone arrays. Our inversion technique successfully discriminates between the single and multiple fracture cases and in all cases accurately identifies the strikes of fracture sets previously imaged using independent methods (borehole image logs, core samples, microseismic event locations). We also generate a synthetic example to highlight the pitfalls that can be encountered if it is assumed that only one fracture set is present when splitting data are interpreted, when in fact more than one fracture set is contributing to the anisotropy.  相似文献   

Impacts of projected climate change on sediment yield and dredging costs          下载免费PDF全文

Travis A. Dahl  Anthony D. Kendall  David W. Hyndman 《水文研究》2018,32(9):1223-1234

Changes in climate may significantly affect how sediment moves through watersheds into harbours and channels that are dredged for navigation or flood control. Here, we applied a hydrologic model driven by a large suite of climate change scenarios to simulate both historical and future sediment yield and transport in two large, adjacent watersheds in the Great Lakes region. Using historical dredging expenditure data from the U.S. Army Corps of Engineers, we then developed a pair of statistical models that link sediment discharge from each river to dredging costs at the watershed outlet. Although both watersheds show similar slight decreases in streamflow and sediment yield in the near‐term, by Mid‐Century, they diverge substantially. Dredging costs are projected to change in opposite directions for the two watersheds; we estimate that future dredging costs will decline in the St. Joseph River by 8–16% by Mid‐Century but increase by 1–6% in the Maumee River. Our results show that the impacts of climate change on sediment yield and dredging may vary significantly by watershed even within a region and that agricultural practices will play a large role in determining future streamflow and sediment loads. We also show that there are large variations in responses across climate projections that cause significant uncertainty in sediment and dredging projections.  相似文献   

Water Level Declines in the High Plains Aquifer: Predevelopment to Resource Senescence   总被引：1，自引：0，他引：1       下载免费PDF全文

Erin M. K. Haacker  Anthony D. Kendall  David W. Hyndman 《Ground water》2016,54(2):231-242

A large imbalance between recharge and water withdrawal has caused vital regions of the High Plains Aquifer (HPA) to experience significant declines in storage. A new predevelopment map coupled with a synthesis of annual water levels demonstrates that aquifer storage has declined by approximately 410 km³ since the 1930s, a 15% larger decline than previous estimates. If current rates of decline continue, much of the Southern High Plains and parts of the Central High Plains will have insufficient water for irrigation within the next 20 to 30 years, whereas most of the Northern High Plains will experience little change in storage. In the western parts of the Central and northern part of the Southern High Plains, saturated thickness has locally declined by more than 50%, and is currently declining at rates of 10% to 20% of initial thickness per decade. The most agriculturally productive portions of the High Plains will not support irrigated production within a matter of decades without significant changes in management.  相似文献